Transtissue drug delivery is a non-invasive therapeutic method in which a drug is first placed onto a tissue of a host animal and then caused to penetrate into the tissue in furtherance of the desired therapeutic treatment. Transtissue drug delivery can be used to treat topical, local, or systemic medical conditions. Delivery can occur across a number of different tissues including the skin, mucosal membranes, or the like. Delivery through the skin is generally referred to as "transdermal" drug delivery.
Transdermal drug delivery is typically accomplished by using a covering element in the form of a transdermal patch device that is attached to the host at the desired drug delivery site. A conventional "peel and place" transdermal patch device generally includes a drug-in-adhesive layer sandwiched between an impermeable backing and a release liner. At the time of use, the release liner is easily removed so that the patch can be attached to the host, adhesive side down. The impermeable backing thus traps the drug between the backing and the attachment site of the host. Over time, the drug penetrates into the host, or is topically active, in furtherance of the desired therapeutic treatment. Optionally, the drug-in-adhesive formulation may include one or more compounds known as penetration enhancers that increase the permeability of the tissue to the drug.
Although the peel and place type of transtissue drug delivery device has been an extremely effective means to accomplish drug delivery for a wide variety of medical conditions, there are still a number of ways in which transtissue drug delivery could be improved. For instance, the structure of the conventional peel and place patch currently involves a manufacturing operation requiring the drug-in-adhesive to be coated onto a substrate, such as the release liner or the impermeable backing as the case may be. This kind of coating step involves substantial expense in terms of capital equipment, utilities, manufacturing space, and human resources needed to carry out the coating operation. To avoid such expense, it would be desirable if a way could be found to eliminate the need for such a coating step.
As another example, the use of a release liner is less than environmentally friendly in the sense that the release liner becomes an item of waste that must be discarded in some fashion after being removed from its patch. It would be desirable if a way could be found to avoid this kind of waste.
Another area of improvement concerns the ability to more effectively control the rate of drug delivery. For current patches, the rate of drug delivery is initially relatively high when the concentration of the drug in the patch is still relatively high. However, as the drug is depleted, the rate of drug delivery slows down. It would be desirable to provide a patch that is characterized by a steady, consistent rate of drug delivery over a longer period of time.
Assignee's co-pending U.S. patent application entitled SPRAY ON BANDAGE AND DRUG DELIVERY SYSTEM having docket number 53867USA5A and filed Aug. 20, 1998 (incorporated herein by reference in its entirety), describes a novel "patch in a bottle" technology in which a fluid composition, e.g. an aerosol spray, is applied onto a substrate as a fluid, but then dries to form a composite covering element, such as a patch, having a tack free outer surface covering an underlying adhesive that helps adhere the patch to the substrate. The fluid compositions have a unique chemical formulation that allows such composite patches to form in situ. Specifically, the fluid compositions include a tacky component, such as an adhesive, and a film forming, non-tacky component. The non-tacky and tacky components are selected to be immiscible with each other so that the components undergo phase separation as the fluid composition dries. The non-tacky component has characteristics that cause it to seek the surface of a coating, where it dries to form a non-tacky protective film. The tacky component dries below this film, providing the bottom surface of the patch with a sufficient tack to adhere to the substrate. One or more pharmacologically active agents are easily incorporated into the fluid compositions so that the fluid compositions and corresponding patches can be used for transtissue drug delivery, e.g. transdermal drug delivery, delivery through a mucosal membrane, or the like.
When applying the patch in bottle formulations to a host in which such formulations include a pharmacologically active agent, it is important that the application of the formulations be accurately controlled so that the patient receives a proper dosage. What is needed is a way to administer these formulations in a manner that allows such control.